Metal cans are transported to a brewery on pallets which contain superimposed layers or tiers of the empty open-topped cans. The layers of cans are mechanically unloaded from the pallet onto a conveyor system which conveys the cans to the filling machine. As the layers of cans are swept from the pallet onto the conveyor, cans may be tipped or downed, and if a downed can is not removed prior to filling, it can create a jam-up in the filling machine which makes it necessary to stop the entire conveying system and manually remove the jammed can.
In the past, vacuum devices have been used to automatically detect and reject downed cans. With devices of this type, a vacuum is applied to the open upper end of upright cans to hold the cans against a moving conveyor, while the downed cans will not be held against the vacuum mechanism and are rejected to a collection location.
Recently there has been increased use in aluminum cans in the brewing industry. Because of the light weight of the aluminum cans, the cans are more susceptible to denting, distortion, or other damage. If a can is dented, the upper flange of the can may not be planar which can cause jamming in the filling machine, or if the can is capped, it can cause a potential leakage problem. Furthermore, dented cans have an unattractive appearance to the consumer. As the cans are travelling in mass at high speed on the conveyor, it is extremely difficult to visually detect slightly damaged cans and to remove the cans from the conveyor.